1. Field of the Invention
The present invention generally relates to the collection of gaseous or liquid phase materials and, more particularly, to the trapping of refrigerant fluids when removed from refrigeration or air-conditioning systems while preventing venting of the refrigerant materials to the atmosphere.
2. Description of the Prior Art
Refrigeration systems, including heat pumps and air-conditioning systems have been in widespread use in the United States and other countries for many years. These systems, which provide for heat transfer between heat exchangers by alternately compressing (e.g. condensing) and decompressing (e.g. evaporating) a refrigerant fluid, are generally quite reliable and will operate with minimal service for periods of several years at a time. However, when service is required, the entire system must have the refrigerant removed before service can be performed.
In the past, it was often the practice to simply vent the refrigerant to the atmosphere, which could be done in a very short time by simply cutting or otherwise opening a tube in which the refrigerant was carried. More recently, however, it has been discovered that this practice represents a substantial environmental hazard. Specifically, most common refrigerant materials, notably chlorinated fluorocarbons (CFC's) such as Freon.TM., are believed to catalyze the destruction of ozone molecules in the atmosphere and may otherwise react with other atmospheric gases, as well.
Ozone concentrations in the atmosphere are of particular concern since ozone reduces the transmission of the ultraviolet (UV) portion of sunlight to the earth's surface and depletion of ozone has thus been linked to increased incidence of skin cancer in humans in recent years. The action of CFC's is particularly severe since it appears to catalyze reactions of ozone rather than directly reacting therewith. These CFC molecules are generally quite stable and it has been theorized that a single molecule of a CFC propellant or refrigerant may catalyze the decomposition of ten thousand molecules of ozone or perhaps many times that number.
CFC materials have also been used as propellants in aerosol dispensers. Such use is now forbidden in the United States and some other countries, but use as propellants still continues in many parts of the world. Therefore, in circumstances where collection of CFC's is possible, it is critically important that collection be complete and venting of CFC's into the atmosphere eliminated.
Accordingly, in recent years, numerous arrangements have been proposed and used in practice to collect refrigerant materials from refrigeration systems. However, these systems often allow a percentage of the refrigerant to escape into the atmosphere. Since some refrigeration systems are quite large, even small percentages of escaping refrigerant can represent quite substantial amounts of refrigerant material. Also, for some small systems such as in a home refrigerator or an automobile, the percentage of refrigerant which escapes is often much larger since the tubes for connection of any refrigerant collection system (and from which refrigerant cannot be collected in prior arrangements) represent a comparatively large volume.
Further, these collection arrangements are inherently quite slow when used properly to minimize escape of refrigerant, causing a 300% increase in the time required for performing service on a refrigeration system. For example, in servicing of an air conditioning system, a collection system is typically connected to the refrigeration system at service valves provided therein. When these service valves are opened, the refrigerant, if above atmospheric pressure, will flow spontaneously to the collection vessel. Thereafter, pumping of the refrigerant is done to pressurize the refrigerant in the collection vessel and to draw a partial vacuum in the refrigeration system in order to extract the refrigerant. This pumping process is slow and requires specially designed pumps since in the latter stages of the operation, the pump is operating to pump material from a substantial level of vacuum to a relatively high pressure. A fairly high degree of vacuum is required by regulation at the present time (10 inches of mercury, soon to be increased to 20 inches of mercury). Nevertheless, some refrigerant remains in the refrigeration system and in the tubes between the pump and the collection vessel. This refrigerant is then lost to the atmosphere.
Additionally, the collection vessels must not be overfilled since the degree to which a collection vessel may be safely filled is a function of the pressures it is designed to withstand. Therefore, refrigerant in overfilled collection vessels will not be purchased for recycling since overfilled vessels present the danger of an explosion. Thus, collection of refrigerant from a large system requires monitoring of the amount of collected material by trained personnel and periodic stopping of the collection process and substitution of collection vessels. Additional refrigerant is lost to the atmosphere at each change of collection vessels since they must be disconnected from the collection system while the connection tubing is filled with pressurized refrigerant.
Air-conditioning systems are also known which operate at less than one atmosphere pressure using so-called Freon R 113.TM., which is a liquid at room temperature and atmospheric pressure. Collection of refrigerant from this type of system relies on passing gases, containing the refrigerant, in the vapor state, from a tank into a water-cooled heat exchanger in which any vapor phase refrigerant is theoretically condensed and flows back under the influence of gravity to the tank while uncondensed gases are vented. However, such flow is impeded by the gas flow and a portion of the refrigerant may again be evaporated. Therefore, it is estimated that the portion of refrigerant which escapes to the atmosphere may be as high as 10% to 20% of the portion collected by this apparatus.
This system, which relies on condensation of the refrigerant at a temperature only slightly below the boiling point of the refrigerant, also requires several hours to process the contents of a moderate sized refrigeration system. Such an extended period of time, during which the system must be operated by skilled personnel increases the cost of service to the refrigeration system. Further, it reduces the number of units which can be serviced by such personnel by about two-thirds compared to the prior practice (e.g. two units instead of six units per day) when the refrigerant was merely vented to the atmosphere. Therefore, there is a substantial pecuniary incentive to use the apparatus improperly, resulting in increased amounts of refrigerant released into the atmosphere. Such improper use of the apparatus and the deleterious effects of such improper use are the direct result of reliance on a heat exchanger which is open to the atmosphere to condense all refrigerant in the gases passed therethrough. Clearly, if gases are passed too rapidly through the heat exchanger, complete condensation cannot take place. Further, if the flow rate of such gases is further increased, the flow of gases may counteract the counter flow of condensed refrigerant or even cause liquified refrigerant to be re-evaporated and/or ejected from the heat exchanger. At the present time, there are no feasible or effective safeguards against improper operation of this type of collection apparatus and only a separate detector of the refrigerant material would be able to determine whether or not refrigerant was, in fact, being vented. The provision of such a detector would be of marginal value since the collection apparatus, even if properly operated, is incapable of collecting all of the refrigerant. The amount of refrigerant allowed to escape might be reduced to low concentration levels by low flow rate and yet permit a substantial quantity of refrigerant to escape over a period of time. In short, the present state of the art imposes a trade-off between the rate of refrigerant collection and the amount of refrigerant which is allowed to escape into the atmosphere. The limitations of current collection equipment effectively encourage faster collection rates with the result of greatly increased amounts of released refrigerant.
It has been found by the inventor that the above described apparatus can be made to function more efficiently by reducing the temperature at which the heat exchanger is made to operate. However, complete collection of refrigerant is still not achieved. Other low temperature and cryogenic gas collection arrangements are also known in the art such as are disclosed in U.S. Pat. Nos. 4,150,494 and 4,424,680 to Rothschild. However, a major concern in the operation of such systems is the prevention of freezing of the condensible gas as it is introduced into the vicinity of the cryogenic material. Such freezing may entirely block flow of the condensible gas and halt the collection process. The only alternative in such a case is to substitute collection apparatus and to continue the process with the substituted apparatus; a time consuming and apparatus intensive option which also causes some release of material to be collected. Accordingly, the rate of collection of gases and the proximity of the collected gas and the cryogenic material, such as liquid nitrogen, is carefully controlled in much the same manner as with the heat exchanging condenser in the system described above. In fact, arrangements such as passing the collected gases over the surface of the cryogenic material (as in U.S. Pat No. 4,150,494 to Rothschild) or spraying a liquid cryogenic material into a stream of gas to be collected (as in U.S. Pat. No. 4,424,680 to Rothschild) are merely different forms of heat exchanging condensers. Either of these arrangements only improve upon the efficiency of the above described apparatus by virtue of the lower available temperature at which the heat exchange takes place. Both rely on regulation of the flow rate of the gas to be collected and neither provides any selective barrier to the escape of gases to be collected or inherent safeguard against the misuse of the collection apparatus.
As further background, at the present time, refrigerants are collected in the field using portable tanks containing air. The refrigerant is mixed with the air in the container as the refrigerant is pumped or displaced from the refrigeration system and is thus contaminated. Apparatus used to transfer refrigerant from the collection containers to a larger tank, either in the field or at a refrigerant recycling facility presents a further opportunity for loss of refrigerant to the atmosphere. Therefore, there are several points in the present collection process where refrigerant is likely to be vented to the atmosphere.